Calcium hypochlorite of reduced reactivity

ABSTRACT

The present invention describes a solid calcium hypochlorite product formulation, including a polymeric alkali salt, which formulation exhibits improved environmental stability and shelf-life while simultaneously inhibiting scale in dispensing equipment, as well as in and on feed equipment used for delivering a calcium hypochlorite solution to a water stream which is to be treated.

RELATED APPLICATIONS

[0001] This application claims the benefit under 35 U.S.C. § 120 of U.S.patent application Ser. No. 09/927,430, entitled “CALCIUM HYPOCHLORITEOF REDUCED REACTIVITY,” filed on Aug. 9, 2001, which is hereinincorporated by reference in its entirety.

FIELD OF THE INVENTION

[0002] This invention relates to calcium hypochlorite blends;particularly to blends of solid calcium hypochlorite in combination withan alkali salt form(s) of anti-scaling polymers, wherein the polymer(s)are present in an alkali salt form effective at reducing the hygroscopiccharacteristics of the solid polymer(s), and subsequent calciumhypochlorite blend. This invention also relates to a means of reducingthe reactivity of solid calcium hypochlorite with the said polymer(s) byapplying a coating of the polymer(s) to the solid calcium hypochlorite.

BACKGROUND OF THE INVENTION

[0003] U.S. Pat. Nos. 5,112,521 and 5,004,549 disclose the blending ofPhosphono-Butane-tricarboxylic acid (PBTC) with calcium hypochlorite toproduce a solid calcium hypochlorite blend that inhibits scale formationassociated with the reconstitution and dispensing of the calciumhypochlorite solution.

[0004] U.S. Pat. No. 6,146,538, the contents of which are hereinincorporated by reference, discloses the use of Polymaleic acid (PMA)and/or Polyepoxysuccinic acid (PESA) in an alkali salt form that isblended with calcium hypochlorite to reduce or eliminate scale formationassociated with the reconstitution and dispensing of the calciumhypochlorite solution.

[0005] It is known that increased moisture, especially localizedmoisture, increases the rate of decomposition of calcium hypochlorite.During decomposition, oxygen is released, with chlorides and chloratestypically being the resulting byproducts. In the presence of sufficientmoisture, exothermic reactions result, oxygen release increases, and apotential fire hazard is produced when fuel sources are available, e.g.cloth, hydrocarbons and the like.

[0006] PBTC disclosed in U.S. Pat. Nos. 5,112,521 and 5,004,549, whencombined with calcium hypochlorite as an anti-scaling agent, cannevertheless compromise manufacturing safety and solid productstability, due to its inherent hygroscopic characteristics.

[0007] It has now been discovered that the alkali salt forms of PMA,PESA, and similar polymeric salts which are commonly employed as depositcontrol agents, can significantly reducing the hygroscopiccharacteristics of calcium hypochlorite when combined therewith, inaddition to providing enhanced anti-scaling properties. It has beenfurther discovered that a coating of these polymers or blends thereofsignificantly reduces the reactivity of the solid calcium hypochloriteblend.

[0008] Thus, a step forward in the art is realized via provision of asolid calcium hypochlorite combination which simultaneously exhibitsanti-scaling properties and reduced hygroscopic and reactivitycharacteristics. Such a composition yields improvements in bothmanufacturing safety and product stability by reducing moistureadsorption and subsequent decomposition of the calcium hypochlorite, aswell as improved safety by reducing the reactivity of the solid calciumhypochlorite.

DESCRIPTION OF THE PRIOR ART

[0009] U.S. Pat. No. 4,146,676 describes calcium hypochlorite particlescoated with about 4 to 45 percent by weight of a low melting inorganicsalt, e.g. aluminum sulfate hydrates, to reduce dusting during handlingand to increase stability of calcium hypochlorite contacted with lightedcigarettes or reactive organic materials such as glycerine.

[0010] U.S. Pat. No. 4,965,016 describes a granular calcium hypochloritecomposition comprising a particle of calcium hypochlorite, the surfaceof which has been covered with a double decomposition product of calciumhypochlorite and an alkali metal hydroxide. It was shown the granularstrength and stability was enhanced.

[0011] None of the prior art describes addition of an alkali salt of anorganic polymeric anti-scaling agent to provide improved depositcontrol, while reducing the stability and reactivity of the solidcalcium hypochlorite.

SUMMARY OF THE INVENTION

[0012] The instant invention is directed toward a solid calciumhypochlorite product formulation and a method for its production, whichproduct exhibits improved environmental stability and shelf-life whilesimultaneously inhibiting scale in dispensing equipment, as well as inand on feed equipment used for delivering a calcium hypochloritesolution to a water stream which is to be treated.

[0013] A solid calcium hypochlorite composition with improvedhygroscopic and reactivity characteristics is formulated comprisinghydrated calcium hypochlorite and an alkali salt of Polymaleic acid,Polyepoxysuccinic acid or mixtures thereof, having between 0.01 and 10%by weight of said alkali salts, an available chlorine concentration ofat least 30% and water in the range of about 2% to about 20% by weight.

[0014] In a particularly preferred embodiment, the composition is asolid having greater than about 50% active Calcium Hypochlorite whichexhibits anti-scaling characteristics and reduced hygroscopicity andreactivity.

[0015] The solid calcium hypochlorite may be coated and/or encapsulatedwith at least one polymeric alkali salt selected from within the groupincluding polymaleate, polyacrylate, polyacrylamide, polycarboxylate,Carboxylate-Sulfonate copolymer, Maleic Anhydride copolymer,Polyepoxysuccinate, maleate-sulfonate copolymer, maleate-phosphonatecopolymer, carboxylate-phosphonate copolymer, and/or mixtures thereof.

[0016] The alkali salt may be selected from the at least one of thegroup including the sodium, potassium, lithium, calcium, or magnesiumsalts and mixtures thereof. Additionally, the polymeric alkali salt maybe in a liquid, slurry, or solid form.

[0017] At some point in the manufacturing process the calciumhypochlorite may be formulated/treated with a deposit control agentincluding at least one alkali salt(s), e.g. sodium, potassium, lithium,calcium, magnesium and/or mixtures thereof, of polymaleic acid,polyepoxysuccinic acid, maleic anhydride copolymer,phosphinopolycarboxylic acid, carboxylic-sulfonic acid copolymer,maleic-sulfonic acid copolymer, maleic-phosphonic acid copolymer,carboxylic-phosphonic acid copolymer, and/or mixtures thereof. Theweight percent of deposit control agent is within the range of about0.01% to about 10% of the final weight of the formulated calciumhypochlorite product.

[0018] These polymers and copolymers will exhibit similar hygroscopiccharacteristics in the desired salt forms while providing depositcontrol capability. Furthermore, all are hydrophilic and possess highthermal stability. Therefore they will reduce reactivity of the solidcalcium hypochlorite product.

[0019] Accordingly, it is an objective of the instant invention toprovide a solid calcium hypochlorite product and a method for itsproduction, wherein the resultant product exhibits reduced hygroscopiccharacteristics thereby improving the manufacturing safety andshelf-life and anti-scaling properties of the solid product.

[0020] It is a further objective of the instant invention to provide acoated or encapsulated solid calcium hypochlorite product having reducedreactivity and anti-scaling properties.

[0021] Other objects and advantages of this invention will becomeapparent from the following description taken in conjunction with theaccompanying drawings wherein are set forth, by way of illustration andexample, certain embodiments of this invention. The drawings constitutea part of this specification and include exemplary embodiments of thepresent invention and illustrate various objects and features thereof.

DETAILED DESCRIPTION

[0022] As illustrated in Table 1, embodiments disclosed in U.S. Pat.Nos. 5,112,521 and 5,004,549 as well as an alkali salt form of thePolymaleic acid disclosed in U.S. Pat. No. 6,146,538 (all of which areherein incorporated by reference) were tested for their hygroscopicproperties by exposing similar quantities of each to a controlledatmospheric environment consisting of the following approximateconditions:

[0023] 70° F., and 50% humidity.

[0024] The samples were weighed and then exposed to the controlledenvironment. The samples were weighed before and after exposure. Theincrease in weight is associated with the increased moisture.

[0025] The NaPBTC increased moisture through adsorbing moisture from thesurrounding environment.

[0026] It is understood that based upon the known reactivity of calciumhypochlorite, which is a Class 3 oxidizer, and its known increaseddecomposition with increased moisture, that the addition of ananti-scaling agent that increases hygroscopicity will lead to apotentially dangerous situation. Thus, the instant invention provides acombination of ingredients which simultaneously reduces the hygroscopiccharacteristics of the final solid product, thereby improving themanufacturing safety and final product stability, while ensuringchemical feed reliability through improved deposit control. TABLE 1Weight Weight After w/w % Change Before 2 hr. 2 hr. Dry Polymaleate 0.99grams 1.01 grams  2.02% Polymer 1.09 grams 1.27 grams 16.51% BAYHIBIT(PBTC) Weight w/w % Change After 24 hr. 24 hr. Dry Polymaleate 1.06grams  7.07% Polymer 1.93 grams 77.06% BAYHIBIT (PBTC)

[0027] Adsorption of localized moisture creates the greatest concern.While the % weight increase to a 1.5% blend would appear to be minimal,localized moisture increase will correlate to the data exemplified inTable 1, reducing shelf life, chlorine activity, and potential increasedrisk of combustion when fuel sources are contacted as outlined in Table2, below.

[0028] While not wishing to be bound to any particular physical form,the combination of calcium hypochlorite and polymer may be in the formof a homogeneous mixture, may alternatively take the form of an outerlayer or covering which coats or encapsulates the cal-hypo for increasedstability and reduced reactivity, or a combination thereof.

[0029] Table 2 illustrates the reaction of 68% calcium hypochloriteshock, sold under the brand name HTH SHOCK, with and without a coatingof a calcium polymaleate salt, upon exposure to oil.

[0030] Each sample used approximately 7.5 grams of solid calciumhypochlorite. The treated sample was mixed with 4.7 grams of polymersalt (slurry weight), followed by convective drying. Each sample wasplaced in a dish where 1 oz. of oil (brake fluid) was added as a fuelsource.

[0031] The results clearly illustrate that coating the solid calciumhypochlorite with a polymeric salt(s) of Polymaleic acid or PESA asdescribed in U.S. Pat. No. 6,146,538 dramatically reduces the reactivityof calcium hypochlorite. Even in the case of extended exposure tocombustible materials, the formulation described has the ability tosignificantly reduce the rate of decomposition of the calciumhypochlorite and prevent ignition when ignition would otherwise occurwithout treatment. It is therefore also reasonable to extrapolate fromthe data that further improvement would be achieved by encapsulation ofthe solid calcium hypochlorite. TABLE 2 Time to Time to FumingCombustion Residue HTH Shock 58 62 Charred, light seconds secondsweight, ash like residue Treated HTH Shock 525 Not No charred, secondsapplicable heavy, polymer cal-hypo mix

[0032] Additional tests were performed using various polymeric saltswith known anti-scaling abilities. These polymers all possess thermalstability sufficient to prevent their decomposition during exposure toexothermic reactions from the decomposition of exposed calciumhypochlorite as well as hot fuming fuels. The thermal stability ensuresthe polymer coating prevents exposure of coated calcium hypochloritethereby preventing a self-sustaining decomposition or runaway reaction.

[0033] Salt samples of polyacrylate and polymaleate were produced forreactivity testing in Table 3. TABLE 3 Polymer Salt Grams 68% GramsPolymer Sample Form Cal-Hypo (solids) 1 Na/Ca Polyacrylate 45 Approx. 22 Ca Polyacrylate 45 Approx. 2 3 Na/Ca Polymaleate 45 Approx. 2

[0034] These polymer salt samples were applied in either the form of aslurry or foam to 45 gram samples of >68% calcium hypochlorite soldunder the brand name HTH. Foam (table 4 sample 3b) was used to enhancethe distribution of the polymer. After drying, the treated samples werecompared to blank samples for reactivity. 10 ml of brake oil fluid wasused as a fuel source, and the time from addition to fuming and ignitionwas measured along with their weights.

[0035] Table 4 illustrates the results of the testing. TABLE 4 Cal-hypoFinal wt. Total wt. Fuming Ignition Weight Polymer Sample (gm) (gm)(sec) (sec) (gm) Appearance applied Untreated 1 7.72 9.99 spilled n/an/a n/a n/a 2 7.84 10.02 12 14 10.13 Charred Ash n/a 3 7.81 9.99 13 15 9.74 Charred Ash n/a 4 7.86 10.03 13 15  9.37 Charred Ash n/a Treated7.88 9.95 100  N/A 15.97 Cal-hypo Slurry residue 7.77 10.03 105  N/A16.8  Cal-hypo Slurry residue 7.89 9.99 45 N/A 14.67 Cal-hypo Slurryresidue 7.88 9.92 195  N/A 18.83 Cal-hypo Foam residue

[0036] The results of these test illustrate that treating the >68%calcium hypochlorite with an alkali salt form of hydrophilic polymerwith thermal stability exceeding 300° F. significantly reduces thereactivity of the calcium hypochlorite.

[0037] The reaction is self-limiting in that only exposed (untreated)calcium hypochlorite is involved in the reaction and once consumed inthe reaction, residual fuel remains in contact with the stabilized(treated) calcium hypochlorite.

[0038] These test results further illustrate that by limiting exposureof calcium hypochlorite to the fuel source, the rate of reaction issignificantly reduced, and ignition is avoided all together.

[0039] Yet another result of these tests is that increased coverage ofthe calcium hypochlorite yields further reduction in reactivity of thetreated calcium hypochlorite. In this example, application of thepolymer by use of an expanded foam to increase its volume improvedcoverage and distribution, correlating to improved performance atreducing the samples reactivity.

[0040] As previously presented, improving the hygroscopiccharacteristics of the calcium hypochlorite improves the manufacturingsafety and shelf-life of the solid product. This is true regardless ofwhether the solid product is in a granular, pellet, tablet or briquetteform. By adding an anti-scaling agent with improved hygroscopiccharacteristics, the potential for compromising safety and shelf-life isreduced.

[0041] By reducing the surface area of the calcium hypochlorite bycoating the solid material with a hydrophilic polymeric salt withthermal stability exceeding 300° F., the reactivity of the calciumhypochlorite is reduced, while allowing rapid dissolution of the calciumhypochlorite when diluted with water, as in the case of a calciumhypochlorite dispenser.

[0042] To further improve the hygroscopic characteristics of thehydrophilic salt, divalent salts, or increased percentages thereof,should be included in the final salt form of the polymer.

[0043] It is to be understood that while a certain form of the inventionis illustrated, it is not to be limited to the specific form orarrangement of parts herein described and shown. It will be apparent tothose skilled in the art that various changes may be made withoutdeparting from the scope of the invention and the invention is not to beconsidered limited to what is shown and described in the specification.

[0044] One skilled in the art will readily appreciate that the presentinvention is well adapted to carry out the objects and obtain the endsand advantages mentioned, as well as those inherent therein. Thecompounds, compositions, and any biologically related compounds,methods, procedures and techniques described herein are presentlyrepresentative of the preferred embodiments, are intended to beexemplary, and are not intended as limitations on the scope. Changestherein and other uses will occur to those skilled in the art, which areencompassed within the spirit of the invention and are defined by thescope of the appended claims.

[0045] Although the invention has been described in connection withspecific preferred embodiments, it should be understood that theinvention as claimed should not be unduly limited to such specificembodiments. Indeed, various modifications of the described modes forcarrying out the invention which are obvious to those skilled in the artare intended to be within the scope of the following claims.

1. A method for applying a polymeric alkali salt to reduce thehygroscopic and reactivity characteristics of a solid calciumhypochlorite particle comprising: providing a solid calcium hypochloritein a particle form: applying at least one polymeric alkali salt to saidsolid calcium hypochlorite in an amount sufficient to reduce reactivityof said calcium hypochlorite during at least one phase of a calciumhypochlorite manufacturing process.
 2. The method in accordance withclaim 1, wherein: said polymeric alkali salt is applied in the form of aslurry.
 3. The method in accordance with claim 1, wherein: saidpolymeric alkali salt is applied in the form of a solid.
 4. The methodin accordance with claim 1, wherein: said polymeric alkali salt isapplied in the form of a foam.
 5. The method in accordance with claim 1,wherein: said polymeric alkali salt is applied in the form of a liquid.6. The method in accordance with claim 1 further including: addition ofa deposit controlling effective amount of an agent selected from thegroup consisting of at least one alkali salt of a compound selected fromthe group consisting of polymaleic acid, polyepoxysuccinic acid, maleicanhydride copolymer, phosphinopolycarboxylic acid, carboxylic-sulfonicacid copolymer, maleic-sulfonic acid copolymer, maleic-phosphonic acidcopolymer, carboxylic-phosphonic acid copolymer, or mixtures thereof.